The present invention relates to a gas sample introduction device for introducing sample gas to a gas analyzer such as a gas chromatograph and a gas chromatograph using the same.
In a gas chromatography analysis for a sample gas, a gas sample introduction device for introducing the sample gas which is a subject of the analysis into a flow of carrier gas supplied to a column, is widely used. For a sample introduction by the gas sample introduction device, there is a system for measuring a predetermined amount of sample gas by a measuring tube provided in a flow path and introducing it to the column; and a system for concentrating the sample gas by a concentration device provided in the flow path and introducing it to the column. Also, a device which can carry out both of the above-mentioned systems by switching is widely used.
FIG. 4 shows the structure of a flow path in a conventional gas sample introduction device with a function of carrying out the gas sample introduction by switching the sample introduction (hereinafter, called a measurement mode) using the above-mentioned measuring tube and the sample introduction (hereinafter, called a concentration mode) using the concentration device. An eight-direction valve 110 can be manually or mechanically switched to two states between a connected state shown in full lines and a connected state shown in dotted lines in FIG. 4. SVa to SVe are electromagnetic valves, and Ta to Tc are branched tubes. Incidentally, NO of each electromagnetic valve represents a normal open port, NC of each electromagnetic valve represents a normal closed port, and C of each electromagnetic valve represents a common port. Incidentally, although a gas inlet 162 and a mass flow controller 150 are used for supplying a predetermined flow rate of pressured gas in a sample container 200 or dry purge gas in a concentration device 130, the details are omitted in this specification.
First, operations at the time of the measurement mode in the device in FIG. 4 will be explained. When the eight-direction valve 110 is set in the connected state shown in the dotted lines and the electromagnetic valves SVd, SVe are set in NO sides (i.e., C sides and NO sides are connected), the sample gas collected from the sample container 200 by a needle 140 passes through a measuring tube 120 via ports d, e, and then, is discharged from a gas outlet 172 via ports h, a, the electromagnetic valve SVd, and the branched tube Ta. Incidentally, carrier gas supplied to a gas inlet 161 from a gas cylinder and the like (not shown) is sent to a column for analysis via the electromagnetic valve SVe, the ports f, g, the branched tube Tc, and a gas outlet 171.
In the state wherein the sample gas is flowed into the measuring tube 120 as mentioned above, the eight-direction valve 110 is switched to the connected state shown in the full lines in FIG. 4. Hereby, the carrier gas passes through the measuring tube 120 via the ports f, e, and a certain amount of sample gas which is determined by the inner volume of the measuring tube 120 retained in the measuring tube 120 is pushed to the carrier gas, and sent to the column for analysis via the ports h, g, and the branched tube Tc. Incidentally, the sample gas sent to the column is separated by each component in a process of passing through the column, and sequentially detected by a detector via the column.
Subsequently, operations at the time of the concentration mode will be explained. When the eight-direction valve 110 is set in the connected state shown in the full lines, the electromagnetic valve SVe is set to an NO side, and also the electromagnetic valve SVc is set to an NC side, the sample gas collected by the needle 140 passes through a collecting tube 131 provided in the concentration device 130 via the ports d, c, and then, is discharged from the gas outlet 172 through the electromagnetic valve SVc and the branched tube Ta. At this time, the collecting tube 131 is cooled down by cooling means (not shown), and in the process wherein the sample gas passes through the collecting tube 131, a predetermined component (sample component) in the sample gas can be absorbed into the collecting tube 131. Incidentally, at this time, the carrier gas supplied from the gas inlet 161 flows into the column via the electromagnetic valve SVe, ports f, e, measuring tube 120, ports h, g, branched tube Tc, and gas outlet 171.
As mentioned above, after the sample component is absorbed into the collecting tube 131, the eight-direction valve 110 is switched to the connected state shown in the dotted lines, the electromagnetic valve SVc is switched to the NO side, and the electromagnetic valve SVe is switched to the NC side. Then, the carrier gas passes through the collecting tube 131 via the electromagnetic valve SVe, branched tube Tb, and the electromagnetic valve SVc in a direction opposite to the previous sample gas. In this state, when the collecting tube 131 is rapidly heated by heating means (not shown), the sample component which has been absorbed into the collecting tube 131 is desorbed at once, so that the sample component in high concentration outflows from the collecting tube 131 with a carrier gas flow, and is introduced to the column via the ports c, b and branched tube Tc. According to the above-mentioned concentration mode, even if the sample component contained in the original sample gas has a small amount, this can be sent to the column after concentration, so that detection sensitivity can be improved.
As mentioned above, in the gas sample introduction device having the conventional function of switching the measurement mode and the concentration mode, the measuring tube 120 and the collecting tube 131 are connected in parallel, and the sample gas which has been sent from one of the measurement mode and the concentration mode flows into the column through the branched tube Tc provided immediately before the column. However, since the gas does not flow in a pipe on a collecting tube 131 side of the branched tube Tc at the time when the measurement mode is carried out, there was a possibility that a part of the sample gas sent from the measuring tube 120 might move into the pipe on the collecting tube 131 side by spreading. Similarly, since the gas does not flow in the pipe on the measuring tube 120 side of the branched tube Tc at the time when the concentration mode is carried out, there was a possibility that a part of the sample gas sent from the collecting tube 131 might move into the pipe on the measuring tube 120 side by spreading. If the sample gas spreads as above, a collection rate (rate between the sample gas introduced to the column and the sample gas collected from the sample container 200) of the sample gas is reduced, so that negative effects can be exerted on analytical sensitivity or analytical precision. Also, the sample gas moved into an unintended pipe may be introduced to the column through the branching tube Tc at the time of the next analysis, and this may have an effect on a result of the analysis.
The present invention has been made in order to solve the above-mentioned problem, and an object of this invention is to provide a gas sample introduction device which can carry out the gas sample introduction by switching between the measurement mode and the concentration mode, prevent the sample gas from spreading to the unintended pipe, and improve the analytical sensitivity or analytical precision in a gas analysis and reliability of the analysis, and the gas chromatograph using the same.
Further objects and advantages of the invention will be apparent from the following description of the invention.